Polymeric foams made from high Tg thermoplastic polymers such as notably polyether sulfones (PES), polyphenylsulfones (PPSU) and polyetherimides (PEI), are typically employed in lightweight applications across multiple market segments such as transport, mobile electronics, building materials, household goods, food service trays and medical, and the like. The growing need to use high Tg thermoplastic polymeric foams especially in light structures, such as for example in structural sandwich panels implies critical properties such as notably thermal resistance, flame resistance, environmental resistance, mechanical strength, low-temperature impact resistance, excellent lightweight, thermal-insulating characteristics, soundproofing characteristics, vibration-proofing characteristics, chemical resistance, and recycling properties.
US 2004/0167241 A1 describes open-cell foams which are composed from high-temperature-resistant thermoplastics selected from the group consisting of polyetherimides (PEI), polyether sulfones (PES), polysulfones, polyether ketones, polyether ether ketones, polyether ketone ketones, polyethersulfonamides, and mixtures of these. The working examples were performed with polyether sulfones (PES) as especially preferred high-temperature-resistant thermoplastic.
US 2004/0212119 A1 discloses a process for producing foam webs by foam extrusion of a mixture of a polysulfone or polyether sulfone and a volatile blowing agent, where the blowing agent is water or a mixture of water with an ancillary blowing agent such as notably an inert gas or organic liquid, e.g. an alcohol or a ketone.
WO 2009/085688 discloses a foam composed of the high heat thermoplastic resin polyetherimides (PEI). Said foams were made by a foam extrusion process.
However, said foams composed of high Tg thermoplastic polymers such as polyetherimides (PEI), polyether sulfones (PES) and polyphenylsulfones (PPSU) still show some drawbacks in the manufacturing of foamed articles which requires very high processing temperatures. For example, in the hot thermosetting resin impregnation process used to produce structural sandwich panels, as mentioned above, temperatures as high as 180° C. are required. Said high temperatures are approaching the heat deflection temperatures of the high Tg thermoplastic polymers like PEI, PES and PPSU resulting in a more problematic retention of foam structural integrity during this high temperature manufacturing step.
Thus, there is still a high need for foam materials comprising high-temperature thermoplastic compositions which can overcome all these drawbacks, as mentioned above, and whereby said foam material are characterized by having improved thermal performance capabilities, in particular more robust resistance to very high temperatures used in the manufacturing of structural foamed articles and having improved chemical resistance such as for example resisting hot liquids that are typically used in the transport industry, like for example jet fuels and hydraulic fluids, in particular Skydrol, while retaining all excellent foam properties such as a well defined and fairly homogeneous cell structure and excellent balance of mechanical properties such as high stiffness and strength properties at a low foam density, higher impact resistance to resist breakage in use, high flame and heat resistance, and whereby the high-temperature thermoplastic foam articles made therefrom have excellent heat resistance, flame resistance, and environmental resistance, mechanical strength, and low-temperature impact resistance, and possesses excellent lightweight, thermal-insulating characteristics, soundproofing characteristics, vibration-proofing characteristics, chemical resistance, and recycling properties.